In a typical inverted tooth chain used in transmission and timing drive applications there are inner link rows and outer link rows of links. The inner link rows will include one or more inverted tooth links that engage the sprocket teeth for the transmission of power. The outer link rows generally will include some conventional inverted tooth links similar to the ones used in the inner link rows and in the outermost position of the outer link rows there will usually be two outer or guide links that help guide the chain on the sprocket by engaging the sides or outer flanks of the sprocket. In some special cases the two guide links are replaced by a single centrally positioned guide link.
As chains become narrower, the space occupied by the two guide links becomes a significant portion of the total space occupied by the chain. To address this issue, certain chains have been devised that engage the sprocket with links of the inner link row only. The outer link rows of such chains generally only include two guide links. These chains are known as xe2x80x9cblock laced chainsxe2x80x9d because they most often include a number of identical sprocket engaging links positioned side by side thus forming a block of links. A modern day example of such a chain is Ledvina U.S. Pat. No. 4,758,210. However, such chains engage the sprockets in less than an optimum manner. Additionally, when conventional chains become narrow, the thickness of the sprocket tooth is further reduced, which creates potential strength concerns. The magnitude of the problem is increased further in instances where the cross section of the sprocket tooth is also decreased to improve the strength of the links.
Noise is associated with any chain drive. While noise is generated from any number of different sources it is the purpose of this invention to address noise generated from the conventional guide links contacting the sides of the sprocket teeth.
Another major problem associated with chains of conventional construction which include sprocket engaging inner links and guide links in the outer link rows is that the strength and elasticity of the conventional links and the guide links vary significantly. Attempts to address this issue via special guide link designs are exemplified by Avramidis U.S. Pat. No. 4,915,675 and Bremer U.S. Pat. No. 2,602,344. Whereas these methods have resulted in measurable improvements, results are better when these methods are applied in transmission chains in which the conventional links are stronger. With the weaker and less rigid links of timing chains and, particularly, the links of narrow timing chains, the results are less successful because the strength discrepancy between the sprocket engaging inner links and the guide links is substantial.
It is therefore the purpose of this invention to arrive at a chain embodiment that allows very narrow configurations without adversely affecting the optimum engagement between chain and sprocket, maintain acceptable sprocket tooth strength and eliminate any mismatches in strength and elasticity between links.
In the present invention, outer link rows are alternately interleaved with conventional inner link rows. The outer link rows are made and the objective of the invention achieved by eliminating conventional guide links in the outer link rows and then combining thick inner links in the inner link rows with thinner links in the outer link rows along with pins of any preferred configuration in a simple assembly. In the simplest embodiment, one thick linkxe2x80x94about twice the normal link thicknessxe2x80x94in the inner link row is interlaced with two standard thickness links in the outer link row. Round, oval, or rocking pins are fit securely into the two thin outer links securing the assembly, typically by press-fitting. The sprocket will be somewhat thicker than the total thickness of the thick link plus the two thin links.
In another embodiment, inner link rows and outer link rows are alternately interleaved. The outer link rows include a pair of outer links, having a standard thickness, which are press fit onto the ends of pins. The outer links have a pair of depending teeth joined by a crotch. The teeth of the outer links have a surface adapted to engage the teeth of a sprocket.
The outer link rows further include a standard thickness center link or inner link positioned between the outer links. The center link has the same form as a conventional inner link and is distinguished by being located in an outer link row. The center link is connected to the outer links by the pins or pivot members but need not be secured to the pins and is free to float, articulate or rotate with respect to the pins.
The inner link rows include a pair of inner links approximately twice the thickness of the outer links. Each inner link is positioned between an outer flank of the center or central link and an outer link. The inner links are connected by but not secured to the pins and thus, are free to articulate or rotate about the pins.
The elimination of the conventional chain guide links requires different means of maintaining the chain on the sprockets. It is therefore a further objective of this invention to develop other alternatives for the purpose of maintaining the chain on the sprockets. In one embodiment the sprockets are modified to include side flange surfaces to constrain the lateral movement of the chain.
In another embodiment it is possible to increase the height of the outermost links in the outer link row so as to guide the chain in a fixed position by having a member external to the chain protrude between the extended links. This is done by extending the top portion of the outer links a first vertical distance above the apertures of the outer links. The top portion of the inner links are extended above the apertures of the inner links a second vertical distance. The first distance (of the outer links) is made greater than the second distance (of the inner links in the inner link rows). Thus, the top portions of the outer links extend vertically more than the top portions of the inner links.
In another embodiment, the first distance (of the outer links) is made less than the second distance (of the inner links). Thus, the top portions of the outer links extend vertically less than the top portions of the inner links. In this case, the top extended portions of the inner links engage a groove formed in the guide member. Some of these embodiments will be described in more detail.
Other objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.